1. Field of the Invention
The present invention relates to an image recording apparatus for recording images, characters, etc. onto a recording medium by using a recording laser head and, more particularly, an image recording apparatus with high reliability, which can execute a high-speed image recording onto a recording medium in a heat mode with the use of an interference type optical shutter which can withstand a high power laser light.
2. Description of the Prior Art
In the image recording apparatus for recording the images onto the recording medium, improvement in the image recording speed is always requested. In particular, in the image recording apparatus for recording the images in unit of pixel (dot) by scanning an optical spot onto the recording medium such as photosensitive material, etc., it is effective in improving the recording speed to record a plurality of dots simultaneously by irradiating a plurality of optical spots simultaneously to the recording medium.
In unexamined Patent Application Publication (JPA) Hei 2-254472, the fixedly scanning type print head has been proposed in connection with such image recording apparatus.
In Patent Application Publication (KOKAI) Hei 4-303817, Patent Application Publication (KOKAI) Hei 4-306620, etc., the optical head which can expose and record a plurality of dots simultaneously has been proposed. More particularly, the optical device (so-called optical shutter array) which has a plurality of prismatic shutter portions made of PLZT and arranged at a predetermined interval along a predetermined direction is provided, then the laser beam emitted from one or more laser light sources is shaped into the wide laser beam along the predetermined direction by the optical system, which is arranged between the laser light source and the optical shutter array, then the polarizing direction of the laser beam transmitted from the shutter portions is changed selectively by the optical shutter array, which is arranged at the beam waist position of the laser beam, then only the laser beam which is transmitted through respective shutter portions of the optical shutter array and has the predetermined polarizing direction can be irradiated onto the recording medium.
In addition, in Patent Application Publication (KOKAI) Hei 9-216417, the optical device which can control the polarization of the incident laser beam in response to the recorded images such that the energy of the incident laser beam can be utilized effectively in recording the image and which has low probability of the failure has been proposed. This optical device is constructed to comprise the light transmitting portion which is made of electro-optical material such as PLZT, etc. and whose length along the traveling direction of the incident laser beam is set constant and which has the successive shape along the predetermined direction intersecting with the incident laser beam, and a plurality of electrode pairs arranged on both sides of the optical transmitting portion to put the optical path of the incident laser beam between them and arranged at a predetermined interval along the predetermined direction.
A configuration of an optical system of an optical head employing the optical device (PLZT device) as the optical shutter is shown in FIGS. 25A and 25B. The optical system of the optical head is constructed to comprise a semiconductor laser 301, a first lens (cylindrical lens) 311, a second lens 312, a first polarizing device 304, an optical device (PLZT device) 305, a second polarizing device 306, a third lens 313, and a fourth lens 314.
A first optical system consisting of the first lens 311, the second lens 312, and the first polarizing device 304 transmits the laser beam, which is emitted from the semiconductor laser 301, into a light transmitting portion consisting of the optical device 305 as a luminous flux which is formed wide along the predetermined direction. Then, the voltage is applied selectively to a plurality of electrode pairs of the optical device 305 by a controlling means (not shown) so as to form the image which is to be recorded on the recording medium 3 (recording member on a drum 2). Accordingly, the polarization of the incident laser beam is controlled in response to the recorded image every luminous flux, which is transmitted via a different portion on the light transmitting portion of the optical device 305, so that the polarization direction is rotated by 45xc2x0 or 135xc2x0. Then, most of the laser beam having the polarization direction of 45xc2x0 is removed from the laser beam transmitted through the optical device 305 by the second polarization device 306. Then, the recording laser beam having the polarization direction of 135xc2x0 is irradiated onto the recording medium 3 via the first optical system consisting of the third lens 313 and the fourth lens 314.
In this while, in the image recording apparatus in the prior art, the normal power semiconductor laser is employed as the light source. The image can be recorded sufficiently practically by the normal power semiconductor laser onto the fast recording medium (photo mode), e.g., photographic film, printing lith film (the silver salt is employed as photosensitive material), etc. However, since the sensitivity is lowered by three to five digits in the transfer type recording medium (heat mode), the irradiation of the laser beam (exposure) is needed for a long time if the normal power semiconductor laser is employed. Therefore, there is the circumstance that, since a processing time from several thousand times to several hundred thousand times must be consumed in the heat mode, the normal power semiconductor laser is not practical.
For this reason, the recording medium of the heat mode is employed, it is desired to use the high output semiconductor laser as the light source. In this case, in the configuration in which the optical device (PLZT device) or the liquid crystal optical shutter (FLC) is used as the optical shutter like the image recording apparatus in the prior art, the power-tolerance property is required for the optical shutter to withstand the high power laser beam. However, even if the liquid crystal or the PLZT device absorbs merely several % of the optical energy emitted from the high output semiconductor laser, the temperature of the liquid crystal or the PLZT device is excessively increased to thus depart from the rated operating temperature. As a result, there is the circumstance that a possibility of the failure of the system is caused.
The present invention has been made in view of the above circumstance in the prior art, and it is an object of the present invention to provide an image recording apparatus with high reliability, which can execute a high-speed image recording onto a recording medium in a heat mode with the use of an interference type optical shutter which can withstand a high power laser light.
In order to overcome the above subject, an image recording apparatus set forth in a first aspect of the present invention, for recording images on a recording medium by modulating a light emitted from a light source by an optical modulation device, wherein the light source comprises a high power laser, and the optical modulator device is comprises a transmission type optical modulator device which optically modulates the light emitted from the light source by an optical interference effect based on an electro-mechanical operation of a flexible thin film.
In this image recording apparatus, since the transmission type optical modulation device (interference type optical shutter) in which the irradiation light from the high power laser is optically modulated by the electromechanical operation of the optical modulation device is employed, absorption of the incident light can be reduced extremely and also the high output-tolerance property against the high power laser can be enhanced rather than the configuration using the optical device and the crystal liquid shutter in the prior art. In addition, the image can be recorded onto the recording medium in the heat mode at high speed.
In an image recording apparatus of a second aspect, the optical modulator device comprises one electrode, other electrode facing to one electrode to put a clearance between them, and a flexible thin film connected to any one of one electrode and other electrode, and deflects the flexible thin film by a coulomb force, which is generated by applying a voltage between one electrode and other electrode, to then modulate the light transmitted through the flexible thin film by an optical multi-layer film interference effect.
In this image recording apparatus, the light transmitted through the flexible thin film can be optically modulated by deflecting the flexible thin film, which is connected to any one of one electrode and the other electrode, by virtue of the coulomb force, which is generated by applying the voltage between one electrode and the other electrode. In other words, in this optical modulator device, the light intensity transmittance can be suppressed low since the flexible thin film is not deformed when the voltage is not applied between the electrodes, while the light intensity transmittance can be increased since the flexible thin film is deformed when the voltage is applied between the electrodes. As a result, the optical modulation can be achieved.
In this case, by using the optical modulator device formed as a laminated structure, for example, the interference type optical shutter utilizing the Fabry-Perot interference, the image recording apparatus with high reliability can be implemented, which can be operated by the lower voltage to have the excellent high-speed responsibility without the problem of heat generation due to the light absorption, and can be formed as the integrated circuit on the semiconductor substrate.
In an image recording apparatus of a third aspect, the optical modulator device is arranged to be inclined relative to a surface, which intersects orthogonally with an incident optical axis from the light source, by a predetermined angle.
In this image recording apparatus, the return light from the optical modulator device can be prevented from entering into the light source by tilting the optical modulator device relative to the surface being intersecting orthogonally with the incident optical axis from the light source by the predetermined angle such that the return light from the optical modulator device is not input into a part or all of the incident light paths. As a result, the output of the light source can be maintained normally.
In an image recording apparatus of a fourth aspect, a shielding plate is interposed in a middle of an optical path of a return light from the optical modulator device such that the return light is prevented from entering into the light source by the shielding plate.
In this image recording apparatus, incidence of the return light from the optical modulator device to the light source can be prevented without fail and also reduction in the optical modulation efficiency can be suppressed since the inclined angle of the optical modulator device can be reduced smaller.
In an image recording apparatus. of a fifth aspect, a polarizing beam splitter and a wavelength plate are provided between the light source and the optical modulator device, polarization directions of an incident light and a return light are changed differently respectively, and thus only the return light is removed from an incident optical axis by the polarizing beam splitter.
In this image recording apparatus, when the incident light from the light source transmits through the polarizing beam splitter and the wavelength plate to output to the optical modulator device, such incident light is circularly polarized (45xc2x0 polarized) by the wavelength plate to then irradiate to the optical modulator device. Then, because the return light from the optical modulator device transmits the wavelength plate again, such return light is circularly polarized (45xc2x0 polarized), so that the polarization direction of the return light is changed by 90xc2x0 from the incident light. When such polarized return light is introduced into the polarizing beam splitter, only the return light is departed from the incident optical axis. In other words, the polarization direction of the return light is changed when the return light transmits through the wavelength plate, so that such return light can be removed from the incident optical axis direction by the polarizing beam splitter because of the change of this polarization direction.
In an image recording apparatus of a sixth aspect, the light source is a broad area laser light source, and the optical modulation device is formed as an optical modulation device array in which a plurality of optical modulator elements are aligned in a one-dimensional fashion.
In this image recording apparatus, multiple spots can be formed by using the broad area laser light source as the light source and also the number of spots which can be irradiated at a time can be increased extremely by using the optical modulation array device in which the optical modulation elements are aligned in a predetermined direction. Therefore, the recording time can be reduced while increasing the recording density.
In an image recording apparatus of a seventh aspect, an alignment direction of the optical modulator elements coincides substantially with a direction which intersects orthogonally with main scanning direction.
In this image recording apparatus, in the recording system wherein the reflected light from the optical modulation device is irradiated to the recording rotating drum while scanning the optical head, in which the light source and the optical modulation device are formed integrally, along the axis direction of the recording rotating drum, a plurality of spots can be formed by using the broad area laser light source in the axis direction (sub scanning direction) of the recording rotating drum, so that the recording speed can be enhanced. In addition, in the recording system wherein the reflected light from the optical modulation device is irradiated on to the recording medium while scanning via the polygon mirror, a plurality of spots can be formed by using the broad area laser light source in the carrying direction (sub scanning direction) of the recording medium, so that the recording speed can be enhanced.
In an image recording of an eighth aspect, the optical modulation device array is arranged to have a direction which is rotated around a normal of a surface of the device by a predetermined angle.
In this image recording apparatus, the distances between the irradiation points by the optical modulator device in the width direction of the recording medium can be substantially narrowed. As a result, the fine linear images with excellent linearity can be achieved.
In an image recording apparatus of a ninth aspect, wherein the optical modulator device is an optical modulator array device whose elements are aligned in a two-dimensional matrix, and the rotation angle xcex8 can be given by tan xcex8=Ph/(nxc3x97Pv) where n is number of rows in a main scanning direction of irradiation points which correspond to optical modulator elements, Ph is a pitch in the main scanning direction, and Pv is a pitch in a sub scanning direction.
In this image recording apparatus, even if alignment pitches of elements of the optical modulation array device are different in the main scanning direction and the sub scanning direction, the rotation angle can be precisely defined.
In an image recording apparatus of a tenth aspect, wherein the optical modulator device is arranged to be inclined relative to a surface, which intersects orthogonally with an incident optical axis from the light source by an angle so as to prevent the return light from the optical modulator device from reaching to the light source.
In this image recording apparatus, incidence of the return light from the optical modulator device to the light source can be prevented without fail and also reduction in the optical modulation efficiency can be suppressed since the inclined angle of the optical modulator device can be reduced smaller.